Vibrator motors for electric dry shavers



1967 R. c. TOWNSHEND 3,296,463

VIBRA'IOR MOTORS FOR ELECTRIC DRY SHAVERS Filed Jan. 28, 1964 UnitedStates Patent 3,296,468 VIBRATOR MOTORS FOR ELECTRIC DRY SHAVERS RoehardChambrey Townshend, Sevenoaks, Kent, England, assignor toMorphy-Richards (Cray) Limited, St. Mary Cray, Kent, England, a companyof Great Britain Filed Jan. 28, 1964, Ser. No. 340,597 Claims priority,application Great Britain, Feb. 2, 1963, 4,350/ 63 8 Claims. (Cl.310-29) This invention relates to vibrator motors for electric dryshavers and other electro-mechanical devices.

Known forms of electric dry shavers have one or more reciprocatingcutters driven by a vibrator motor. The vibrator motor consists of anelectro-magnet more or less rigidly fixed to the case and one ortwooscillating arma tures connected mechanically to the cutters.

A disadvantage of known forms of vibrator motor with one armature isthat movement of the armature reacts on the case and sets up a vibrationwhich is transmitted to the hand of the user.

In order to reduce the vibration of the case and make it morecomfortable to hold in the hand a known form of vibrator motor has twoarmatures, the cutter being mechanically connected to one of them. Thetwo armature assemblies have substantially equal polar moments ofinertia about their respective pivots and are constrained by amechanical linkage to move substantially equally in anti phase. Theresult is that the reactions on the case caused by the oscillations ofthe twoarmature assemblies substantially balance each other out and onlythe small residual difference is transmitted to the hand of the user.

According to the present invention there is provided -a vibrator motorcomprising an electro-magnet assembly, an armature assembly, pivotalmountings for both said electro-magnet assembly and said armatureassembly, .mechanical coupling means from said electro-magnet assemblyto said armature assembly to cause said electromagnet assembly and saidarmature assembly to move in anti-phase about their pivotal mountingsthe one with respect to the other under the constraint of saidmechanical means when said electro-magnet is energized in such a waythat the relative angular movements of said armature assembly and saidelectro-magnet assembly are predetermined by said mechanical means. 7 7

One form of shaver vibrator motor according to the present invention hasthe electro-magnet and the armature assembly including the cutterpivoted about their respective centres of gravity. Normally the polarmoment of inertia of the armature assembly about its pivot is much lessthan that of the electro-magnet. A mechanical linkage is arranged sothat the ratio between the angular movements of the armature assemblyand the electromagnet is the "same as the ratio between the moments ofpolar inertia about their pivotal axes of the electro-magnet and thearmature assembly. The result is that the reactions on the case causedby the oscillations of the electro-magnet and the armature assemblysubstantially balance each other out, and only the small residual difference is transmitted to the hand of the user.

For practical reasons it may not be convenient to pivot the armatureassembly and the electro-magnet about their respective centres ofgravity. However, with their respective pivotal mounting suitablylocated it is still pos sible to attain a good degree of balance andthis system is the one most likely to be required in practice.

In order that the present invention may be clearly understood andreadily carried into effect it will now be described with reference tothe accompanying drawings, in which:

FIGURES 1 and 2 illustrate vibrator motors for an 'ice electric dryshaver according to two examples of the present invention.

The electro-magnet assembly of the vibrator motor shown in FIGURE 1 hasa laminated and U-shaped magnetic core 1, on the limbs of which aremounted two coils 2. The armature assembly has the armature magneticlaminations 3 adjacent to the poles of the electromagnet and ismechanically connected to a cutter represented by the rectangle 4. Thecutter operates in conjunction with a shear plate 32.

The armature is pivotally mounted on 'a frame 5 by means of a pin 6projecting from the frame 5. The electro-magnet is mounted rigidly onthe frame 5.

Fixed to the electro-magnet is an Lbeam 7 made of insulating material. Ametal pin 8 passes through the I-beam 7, and is fixed to it, beinginsulated within the web from the electro-magnet coils, and projectsbeyond the flange faces of the I-beam 7 and beyond the frame 5. The endsof the pin 8 are mounted in bearing fixed to the case 31 of the shaver.Thus the frame 5 and all parts mounted on it can pivot in the case onthe pin 8.

The armature is also mechanically connected to the case by the bridgepiece 10 which has knife edges that bear in V-grooves. One V-groove ismoulded in the case at 11 and the other is formed in the porous sinteredmetal bush 12. The cantilever spring 13 has a fiat bottomed depressionformed in it which allows limited movement of a small ball bearing. Thespring 13 forces the ball bearing against the bridge piece 10 solocating the bridge piece knife edges at the bottom of their respectiveV-grooves.

The springs 14 hear at their outer ends against lugs 15 integral withthe frame 5. At their inner ends they bear against the armature so thatits static equilibrium position is at approximately the mean of itsnormal operative travel. Approximately the greatest amplitude ofoscillation is normally obtained with the equilibirium position arrangedso that the corners of the armature and the electro-magnet laminationsare adjacent, as shown in the figure.

Examination of FIGURE 1 shows that for small angles of movement of thearmature the right hand knife edge of the bridge piece is virtuallystationary relative to the case. This means that relative to the casethe armature virtually rotates about the bridge piece right hand knifeedge while the electro-magnet rotates on the pin 8. It is also clearthat for small angular movements of the armature the angular velocityratio relative to the case between movements of the electro-magnet andthe armature is virtually equal to the ratio between the distance fromthe bridge piece right hand knife edge to the centre of the pin 6 andthe distance between the centres of the pins 6 and 8.

The shaver vibrator motor illustrated in FIGURE 1 has the centres ofgravity of the electro-magnet and armature assemblies some distancebelow their respective pivots, described above, relative to the case.This corresponds to the general conditions referred to in the preambleas being the one most likely to be required to practice.

For the shaver vibrator motor illustrated in FIGURE 1 the conditions forbalance within the terms of the present invention may conveniently becalculated as described below for small angles of movement. Some slightadjustments may be desirable in practice to obtain'the best results withthe normal angular movement of the armature.

The electro rnagnet is assumed to have unit angular acceleration andmoments are taken about the two pivot points described above relative tothe case for the inertial reactive torques exerted by the disparatemoving parts. Normal use is made of the well known parallel axestheorem. Due account is taken of the condition that the shaver cutterreciprocates without rotation while the other major moving componentsoscillate about their pivoted axes. Due account is also taken of thevelocity ratios existing between the moving components.

It is important to note that for the purposes of these particularcalculations neither pivot point is assumed to transmit any force atall.

The two equations obtained may conveniently be manipulated by assumingfigures for all the possible variables except the two distancescontrolling the angular velocity ratio. Then, for each of the twoequations, the value of one distance for given values of the other maybe plotted an a graph. The point where the two lines cross gives thesolution.

FIGURE 2 illustrates a layout which is a modification of that shown inFIGURE 1, but which is similar in principle to that shown therein. Itillustratestypical variations which lie within the scope of the presentinvention.

The electro-magnet assembly of the vibrator motor shown in FIGURE 2 hasa laminated and U-shaped magnetic core 16, on the limbs of which aremounted two coils 17. The armature assembly has the armature magneticlaminations 18 adjacent to the poles of the electro-magnet and ismechanically connected to a cutter represented by the chain dottedrectangle 19. The cutter operates in conjunction with a shear plate (notshown).

The armature is pivotally mounted on a frame 20 by means of a pin 21projecting from the frame 20. The electromagnet is mounted rigidly onthe frame 20.

The springs 22 bear at their outer ends against lugs 23 integral withthe frame 20. At their inner ends they bear against the armature.

A metal pressing or die casting or plastic moulding 24 is fixed (bymeans not shown for clarity) to the left hand lug 23 at one end. At theother end it is fixed by a clamping plate 25 to the electro-magnet. Ballor roller bearings 26 and 27 are located between tracks formed in thepart 24 and in the case, which is indicated by shading. These tracks areall concentric with a line which is the axis of oscillation of all partsrigidly fixed to the frame 20.

The armature is also mechanically connected to the case by the metaltape 28 which with all operatively possible positions of the armaturemeets a cylindrical surface provided for it on the armature,tangentially. Both ends of the tape 28 are reinforced and made so thatthey can swivel at their attachment points allowing the tape to seatevenly on the cylindrical surface. The tape 28 is kept taut by theaction of the spring 29 hearing at one end against the plate 25 and atthe other end against the case. This spring 29 also forces the tracks inthe part 24 against the ball or roller bearings 26 and 27 and the latteragainst the tracks in the case. The cantilever spring 30 normally holdsone end of the tape 28 against the case, indicated by the shaded area,so that the tape connection between the armature and the case issufiiciently rigid. Undue loads on the tape, however, such as due toimpacts between the case and the floor, are relieved by flexing of thecantilever spring 30 away from the adjacent part of the case.

The spring 29 and the two springs 22 are arranged so that the staticequilibrium position of the armature is at approximately the mean of itsnormal operative travel. Approximately the greatest amplitude ofoscillation is normally obtained with the equilibriumposition arrangedso that the corners of the armature and electro-magnet laminations areadjacent, as shown in the figure.

Examination of FIGURE 2 shows that for normal angles of movement of thearmature the parts rigidly fixed to the frame 20 oscillate about theaxis with which the tracks for the ball or roller bearings 26 and 27 areconcentric. The armature, meanwhile, oscillates in the opposite senseabout the pin 21 which is fixed to the frame 20. It is also clear thatfor normal angular movements of the armature the angular velocity ratiorelative to the case between the electro-magnet and the armature isvirtually equal to the ratio between the radius of the cylindricalsurface on the armature under one end of the tape 28 and the distancebetween the centre of the pin 21 and the axis with which the tracks forthe ball or roller bearings 26 and 27 are concentric.

What I claim is:

1. A vibrator motor comprising an electro-magnet assembly, an armatureassembly, pivotal mountings for both said electro-magnet assembly andsaid armature assembly, mechanical coupling means from saidelectro-magnet assembly to said armature assembly to cause saidelectromagnet assembly and said armature assembly to move in anti-phaseabout their pivotal mountings the one with respect to the other underthe constraint of said mechanical means when said electro-magnet isenergised in such a way that the relative angular movements of saidarmature assembly and said electromagnet assembly are predetermined bysaid mechanical means.

2. A vibrator motor according to claim 1 further comprising a containingcase, a frame mounted for small angle oscillatory movement in said caseand to which frame said electro-magnet is rigidly secured and saidarmature is pivoted, and a further yielding pivot for said armatureconnected to said case, the pivoting of said armature to said frameproviding the mechanical coupling from said electromagnet to saidarmature.

3. A vibrator motor according to claim 2, said yielding pivot comprisesa bridge piece having two knife edge bearings, a V seating for oneof'said bearings attached to said case, a V seating for the other ofsaid bearings attached to said armature, and spring means urging saidknife edge bearings into said V seatings.

4. A vibrator motor according to claim 2, comprising tracks on saidframe and said case and bearings'operating on the tracks to permit thesmall angle oscillatory movement of said frame, and spring loads meansbearing on said frame and said case.

5. A vibrator motor according to claim 4 said yielding pivot comprisinga tape attached resiliently to said frame and attached to said armatureand wrapped round an arcuate surface OIl said armature.

6. A vibrator motor according to claim 1 wherein in operation whereofthe amplitude of the movements of said electro-magnet and said armatureare inversely proportional to their respective polar moments of inertia.

7. An electric shaver including a vibrator mot-or ac cording to claim 3,a cutter, said case comprising a shear plate in operationaljuxtaposition with said cutter, said armature being in drivingconnection with said cutter.

8. An electric shaver including a vibrator motor according to claim 5, acutter, said case comprising a shear plate in operational juxtapositionwith said cutter, said armature being in driving connection with saidcutter.

References Cited by the Examiner UNITED STATES PATENTS 2,565,697 8/ 1951Odstrucil 3 l0-29 2,998,648 9/1961 Barron et al. 3 043.1 X 3,105,1639/1963 Camp 31 029 3,155,855 11/1964 Fiitterer 31038 MILTON .O.HIRSHFIELD, Primary Examiner. D. F. DUGGAN, Assistant Examiner.

1. A VIBRATOR MOTOR COMPRISING AN ELECTRO-MAGNET ASSEMBLY, AN ARMATUREASSEMBLY, PIVOTAL MOUNTINGS FOR BOTH SAID ELECTRO-MAGNET ASSEMBLY ANDSAID ARMATURE ASSEMBLY, MECHANICAL COUPLING MEANS FROM SAIDELECTRO-MAGNET ASSEMBLY TO SAID ARMATURE ASSEMBLY TO CAUSE SAIDELECTROMAGNET ASSEMBLY AND SAID ARMATURE ASSEMBLY TO MOVE IN ANTI-PHASEABOUT THEIR PIVOTAL MOUNTINGS THE ONE WITH RESPECT TO THE OTHER UNDERTHE CONSTRAINT OF SAID MECHANICAL MEANS WHEN SAID ELECTRO-MAGNET ISENERGISED IN SUCH A WAY THAT THE RELATIVE ANGULAR MOVEMENTS OF SAIDARMATURE ASSEMBLY AND SAID ELECTROMAGNET ASSEMBLY ARE PREDETERMINED BYSAID MECHANICAL MEANS.
 2. A VIBRATOR MOTOR ACCORDING TO CLAIM 1 FURTHERCOMPRISING A CONTAINING CASE, A FRAME MOUNTED FOR SMALL ANGLEOSCILLATORY MOVEMENT IN SAID CASE AND TO WHICH FRAME SAID ELECTRO-MAGNETIS RIGIDLY SECURED AND SAID ARMATURE IS PIVOTED, AND A FURTHER YIELDINGPIVOT FOR SAID ARMATURE CONNECTED TO SAID CASE, THE PIVOTING OF SAIDARMATURE TO SAID FRAME PROVIDING THE MECHANICAL COUPLING FROM SAIDELECTROMAGNET TO SAID ARMATURE.
 3. A VIBRATOR MOTOR ACCORDING TO CLAIM2, SAID YIELDING PIVOT COMPRISES A BRIDGE PIECE HAVING TWO KNIFE EDGEBEARINGS, A V SEATING FOR ONE OF SAID BEARINGS ATTACHED TO SAID CASE, AV SEATING FOR THE OTHER OF SAID BEARINGS ATTACHED TO SAID ARMATURE, ANDSPRING MEANS URGING SAID KNIFE EDGE BEARINGS INTO SAID V SEATINGS.